voltage regulator problem 2

[brashear]

Hi all,
I am trying to use a fixed 2.7V voltage regulator (MIC5219-2.7YM5), and the voltage output is 1.4V when I wire it according to the datasheet and supply it with anywhere from 2.5V to more than 5V. When I tried putting a load on it (20K), the voltage drops to almost zero. Any idea why this is? I ordered three of these regulators and got the same result when I tried all of them. Thank you.

 

[roydm]

You need to include a sketch.
What is the input voltage to the regulator when you load it up?

 

[Skogsgurra]

Only thing I can guess is that Enable is floating or low. Shall be tied high on these regulators.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[brashear]

Here is the circuit diagram. I tied Enable directly to Vin.

 

[Skogsgurra]

Decoupling? I see no capacotors in your diagram.

Did you see any wild HF oscillation on the output?

Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[IRstuff]

Did you thoroughly read the datasheet? While the Bypass input can be left floating, the output REQUIRES a capacitor to PREVENT oscillation.

TTFN

FAQ731-376

 

[brashear]

I think I put the decoupling cap on at first, but took it out when it didn't work. I will try again. I don't see conceptually how not having the decoupling cap would cause the voltage to drop as soon as I put any load on though...can someone explain this to me? Thanks

 

[Skogsgurra]

HF oscillations and their consequences aren't always easy to understand. Could YOU explain why you left it out? Thanks.

Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[brashear]

because I am an idiot and didn't read the datasheet? haha

 

[Skogsgurra]

OK! That's a good explanation. Does it work now?

Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[Warpspeed]

Don't feel too bad Brashear.
Everyone here has at some stage or other in their career, learned a similar lesson.

 

[brashear]

yup, that fixed it! Thanks everyone

 

[IRstuff]

That's one good reason for having an oscilloscope handy during integration. Many odd things can be readily dispensed with if you can actually see what's what.

TTFN

FAQ731-376

 

[zzzjim]

Op Amps found in everthing these days !